Power management in large-scale datacenters is an important problem. Effective power management reduces both the operating costs of datacenters protects the environment from excessive greenhouse gas emissions. Virtualized datacenters are more energy efficient than physical datacenters due to the consolidation of virtualized computing resources on fewer physical servers. However, increases in the demand for computing power have given rise to additional power management features for virtualized computing platforms. Currently, vendors offer separate power management features that manager power consumption, respectively, for a computing cluster and for an individual host computer. For example, VMware, Inc. distributes Host Power Management (HPM) and Distributed Power Management (DPM) with its vSphere® software offering. HPM saves power by utilizing a processor's ACPI states (i.e., the processor's P-states and C-states) to dynamically place certain parts of the computer system into a reduced power state. By contrast, DPM redistributes VMs among physical hosts in a cluster, which enables some hosts to be powered off completely.
However, with DPM, application performance penalties can be high when the demand for VMs increases rapidly. This is due to the fact that DPM (and similar power management solutions) need to power on hosts that were previously powered off and then redistribute VMs to the newly powered on host. The powering on of a host entails a great deal of delay, as the host components (processors, memory, and storage devices) must become active, and the operating system of the host and applications must be reloaded. This stands in contrast with the relatively small delays experienced with HPM, as modifying P-states and C-states does not involve the same degree of latency. However, HPM focuses only on a single host computer and lacks the cluster power management capabilities of DPM.